In nuclear power stations, steam generators, such as recirculating steam generators and once-through steam generators, are used for heat exchange purposes in the generation of steam to drive the turbines. Primary fluid which is heated by the core of the nuclear reactor passes through a bundle of tubes in the steam generator. Secondary fluid, generally water, which is fed into the space surrounding the tubes receives heat from the tubes and is converted into steam for driving the turbines. After cooling and condensation has occurred, the secondary fluid is directed back into the space around the tubes to provide a continuous steam generation cycle. Due to the constant high temperature and severe operating conditions, sludge accumulates on the lower portions of the tubes and on the tubesheet which supports same. The sludge which is mainly comprised of an iron oxide, such as magnetite, reduces the heat transfer efficiency of the tubes and can cause corrosion. Thus, the tubes must be cleaned periodically to remove the sludge and various types of apparatus and methods are available to accomplish this task.
U.S. Pat. No. 4,566,406 entitled "Sludge Removing Apparatus for a Steam Generator" discloses a manifold which is rigidly attached to the tubesheet and remains in place during conventional operation of the steam generator. A plurality of nozzles on the manifold emits streams of water to break up sludge on the upper surface of the tubesheet. Openings are provided in the walls of the steam generator to remove the slurry.
U.S. Pat. No. 4,079,701 entitled "Steam Generator Sludge Removal System" discloses an arrangement of headers at the elevation of the sludge to be removed from around the tubes in order to establish a circumferential fluid stream at that elevation. A fluid lance moved along a line between the headers emits a fluid jet perpendicular to the line of movement of the fluid lance. The lance may also be rotated as it is moved.
U.S. Pat. No. 4,700,662 entitled "Sludge Lance Wand" discloses a lance for cleaning once-through steam generator tubes. The lance has a fixed radius of curvature thus necessitating manual manipulation of same in order to insert the lance between tubes within the tube bundle in the steam generator.
All of the foregoing apparatus have some inherent disadvantages which prevent them from efficiently removing the sludge which accumulates around the tubes within the tube bundle. Because of this, it has become desirable to develop a sludge lance which can be manipulated so as to easily pass through the openings between adjacent tubes within the tube bundle.